Myriad integrated circuit applications utilize current references. In a subset of such applications, such a current reference circuit must be precise and draw a minimal amount of chip supply current, particularly in applications which employ battery power. One exemplary application involves a physical layer device in an IEEE 1394 compliant chipset.
The IEEE 1394 is a high-speed serial bus standard that enables interconnecting of multiple digital devices in a universal fashion. The architecture for the IEEE 1394 bus standard is scalable and employs a flexible peer-to-peer topology that make the serial bus standard advantageous for connecting various types of devices such as computers to digital audio and video hardware.
The IEEE 1394 standard provides three protocol layers as illustrated in FIG. 1, and designated at reference numeral 10. The three layers include a physical layer 12, a link layer 14, and a transaction layer 16; a serial bus management process 18 then connects to each of the three layers. The physical layer 12 connects to a serial bus connector 20 while the other layers 14 and 16 connect to the application (not shown). The physical layer 12 provides the electrical and mechanical connection between the 1394 compliant device and the 1394 cable. In addition to the actual data transmission and reception tasks, the physical layer 12 provides arbitration to insure that all devices have fair access to the bus (not shown).
The link layer 14 provides a data packet delivery service for two types of packet delivery: asynchronous and isochronous. Asynchronous packet delivery is directed to the conventional “transmit-acknowledge” protocol while isochronous packet delivery involves a real-time guaranteed bandwidth protocol for just-in-time delivery of information. The transaction layer 16 provides support for the asynchronous protocol for write, read and lock commands. For example, a write sends data from the originator to the receiver and a read returns the data to the originator, while a lock command combines the write and read functions by producing a round trip routing of data between the sender and the receiver, including any processing by the receiver.
Lastly, the serial bus management 18 provides configuration control of the serial bus (not shown) to: optimize arbitration timing, guarantee adequate power for devices on the bus, assign which 1394 device is the cycle master, assign an isochronous channel ID, and provide notification of errors.
In one particular exemplary application, the physical layer device 12 is in a low power state, but needs to monitor for a connection. In doing so, the physical layer device 12 is required to transmit periodic tone signals for the connection monitoring. Such tones are required to be transmitted with a precise drive current level to determine when a connection is made to another 1394-type device. In such a context, as well as others, there is a need for a high precision current source circuit which utilizes a minimal amount of power.